gh-46236: Add missing PyUnicode_Resize() doc

Doc/c-api/unicode.rst

@@ -666,6 +666,23 @@ APIs:
    .. versionadded:: 3.3
 
 
+.. c:function:: int PyUnicode_Resize(PyObject **unicode, Py_ssize_t length);
+
+   Resize a Unicode object. The length is the number of codepoints.
+
+   Try to resize the string in place (which is usually faster than allocating
+   a new string and copying characters), or create a new string.
+
+   ``*unicode`` is modified to point to the new (resized) object and ``0`` is
+   returned on success. Otherwise, ``-1`` is returned and an exception is set,
+   and ``*unicode`` is left untouched.
+
+   .. warning::
+
+      The function doesn't check string content, the result may not be a
+      string in canonical representation.
+
+
 .. c:function:: Py_ssize_t PyUnicode_Fill(PyObject *unicode, Py_ssize_t start, \
                         Py_ssize_t length, Py_UCS4 fill_char)
 

Doc/data/refcounts.dat

@@ -2791,6 +2791,10 @@ PyUnicode_CopyCharacters:PyObject*:from:0:
 PyUnicode_CopyCharacters:Py_ssize_t:from_start::
 PyUnicode_CopyCharacters:Py_ssize_t:how_many::
 
+PyUnicode_Resize:int:::
+PyUnicode_Resize:PyObject**:unicode:0:
+PyUnicode_Resize:Py_ssize_t:length::
+
 PyUnicode_Fill:Py_ssize_t:::
 PyUnicode_Fill:PyObject*:unicode:0:
 PyUnicode_Fill:Py_ssize_t:start::